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How to Build an LED Planetarium

Everyone loves looking at the stars. Unfortunately, city lights, clouds and pollution often prevent this from being a frequent passtime. This instructable helps capture some of the beauty and most of the romance associated with the heavens and puts it on your living room or bedroom ceiling.

The premise is simple. Make holes in a bowl and shine a light behind it to make stars on the ceiling.

The completion is quite a bit more complex, due to some pesky laws of physics that I'll explain in the next few steps. The end result is a curious looking device that will definitely get lots of remarks, especially when you turn it on.

Unfortunately I didn't think of making an instructable for this until after I had completed the project. It was a gift for a special someone and I didn't want photographic evidence being accidently discovered on my computer or her camera. I'll try my best to be comprehensive and thorough with the pictures I've taken.

This instructable makes minor assumptions that you have basic soldering skills and knowledge of how to use hammers and typical hand tools.

Please vote for me in the Get The LED Out! Competition! Voting ends on June 21st!

Step 1: Materials and Tools

The parts and tools I used for my build are listed below. Naturally you can swap anything out for an equivalent item you think will work just as well. I had a machine shop at my disposal so I made mine entirely of metal. Opaque plastic or wood would do just as well.

Step 2: All-Important Science

The interesting physical property of pinholes is that they function like a lens. This principle is in cameras, projectors, and most notably, our eyes.

In our case, the lensing effect doesn't make a visible change to our lights, since the source is round and the projection is round, through a round hole. The one important thing that must be kept in mind when choosing your light source is this; a wide light source makes a wide projection, and a small light source makes a small projection. We want tiny pinpoint stars, so we want the smallest brightest source possible. The diagrams in this step visualize it for us.

Putting a normal lightbulb inside the bowl will not have the desired effect, so a high powered LED must be used. Also, only 1 LED can be used, or else more than one projection per hole will appear.

Step 3: Making the Constellation Bowl

The first step is punching the holes in the bowl. Drilling was impractical because 1mm drill bits are too fragile to be drilling hundreds of holes in the steel bowl. I bought my bowl for $1 from Dollarama, a thin stainless steel mixing bowl.

Place the dowel in the vice, gripping it very firmly. This piece is going to be the resting piece, and will be destroyed in the process, so don't use expensive wood or something you want to keep.

Print and cut out your constellation chart. You may need to try a couple times printing at different sizes until you find one where your constellations will all fit reasonably well on your bowl. Tape them down with masking tape. Place the bowl on top of the dowel so that the inside of the bowl is resting on the dowel and the outside where your constellation paper is is facing towards the ceiling. Place your center punch on the star, and hit it with the hammer. Practice until you make a hole that is roughly 1mm of open diameter. The surrounding will be slightly dented, and the hole won't be round, but don't worry.

The reason that we hammer from the outside is because the opposite side of the metal will be extremely sharp, so having the sharpness on the inside is better and safer in the end.

After you complete your constellations, feel free to make as many random stars as you'd like. I made enough stars that theres lots to see and the constellations are well hidden, but not lost completely. This part is purely up to you, and you can add more later if you want to.

Step 4: The Skirt

Since the bowl and the base will probably not be light-tight, as was my problem, we need to seal it. We can't seal it permanently, so we need a way to block light that we can remove easily. What I did was punch large holes near the lip of the bowl and rivet a sheet of rubber around the inside. This slides down into the base and blocks the light from the LED that might have escaped through the crack.

You will need to punch four holes around the rim of your bowl that will let you screw it down onto your base. Punch these holes larger than star holes, as big as you need so that your screws can pass through without threading.

Also, the inside of the bowl needs to be painted with black paint. Reflections off the inside can reflect out the opposite side and create strange shapes on your ceiling and walls.

Step 5: Constructing a Base

The base is the next piece of the puzzle. Since the LED has a 120 degree spread, we can't put it level with the lip of the bowl, or we wont have light coming out the holes that are close to the horizon. We need to lower it down about 1.5 inches. I did this by fashioning a metal ring out of sheet metal and making a steel bottom that my LED bolts onto. You could just as easily make a plastic or wooden one if thats easier for you. All that matters is that it is NOT SEE-THROUGH. No light can escape out of anywhere other than our star holes.

Filling the bottom with rubber or painting the inside black is a good way to make sure there are no reflections inside the device. Filling any gaps in the sides or bottom is also crucial, as any escaping light will be visible on your ceiling and walls.

Cut, bend and drill four small brackets that will let you mount your bowl onto your base. Attach them to your base with rivets so that they line up with the four holes you made in your bowl edge.

Your LED needs to be bolted to the bottom of the base, so drill two holes that line up with the notches on the LED that you purchased. Put a tiny bit of thermal grease under the LED so that it conducts its heat into the metal base. If your base isn't made of metal you might want to put the LED on a metal plate in the bottom of your base.

Step 6: The Light Circuit

The circuit is very simple, and consists of three batteries, a resistor, a switch and an LED, all wired in series.

Construct the circuit as shown below. The LED I used was a 3W hex base LED running at 3V and around 1A. The value of R will change depending on what LED you use, and you should be able to calculate the required value using the LED calculator at http://linear1.org/.

Your switch can be mounted anywhere. I put a nice big toggle switch on the front.

Step 7: Stargazing Time!

Screw the bowl down onto the base, and you're done! Turn off the lights and give it a try. If you see strange non-round lights on your ceiling, that means something is reflecting light inside your planetarium. While its on, check the outside for unwanted light leaking out.

I tried to photograph the effect, but without a SLR or tripod capturing the effect well is nearly impossible. The photo does it no justice.

I gave mine to my girlfriend as a birthday gift, and she absolutely loved it. Lying in bed with the Planetarium at your feet is a lot of fun, pointing out the constellations and gazing in wonder. No doubt anyone who recieves one as a gift will be extremely impressed that you made it yourself.

Things to change/improve:

-The result would look better with an even brighter light and even smaller holes
- Having several light sources would allow for more stars with fewer holes, but the ability to have identifiable constellations is lost.
- Adding a wall power adapter would make for a very nice nightlight.

EDIT

Another great add-on would be to add a low-RPM motor on the inside and have the bowl rotate on the light very slowly, just like the actual night sky. I thought of this while building mine but the noise and mechanical issues made me drop the idea pretty quickly, but someone could definitely find a way to do this.

I hope you enjoyed reading my first instructable, thank you very much for reading.

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okay so any help would be greatly appreciated. I am my class president and planning prom. the theme is enchanted forest, and to me the first thing I think is fireflies everywhere. so I want to try to make one of these to project "fireflies" around the room. the only thing is I would ideally want the "fireflies" to rotate around like they're moving around the room, and some come on and some go off. like they do in real life. I had thought I could put something inside the dome that rotates around inside to block one side of holes for a min then rotate around and block the other side. can anyone think of a way I could do that? pleease

I would recommend finding a small slow moving motor like one from a microwave for the turntable inside. those usually run about 5-6 rpm. Using a motor like that to make a rotating base would make all the projections rotate. to selectively obscure some, i would make the projector stationary and use that same motor to rotate a large upside down bowl over top of the projector. cut a slot in the bowl as big as you need to let the light through. somehow youll have to make a platform that would let the bowl rotate but not the projector, which is not that easy with a simple motor.

youll need to make it very bright for it to be seen in a big room with other lights on.

i will be purchasing styro foam hollow balls that come in two halves for my 18" diameter globe projector... main two things are this: can anyone suggest a round night sky map that would fit an18" ball? that and a very bright led light that is small and safe enough to mount inside of such an enclosure i would appreciate it :)

Surplus low speed AC or DC motors are pretty easy to find. They use several gears to reduce the output shafts rotation speed to a few RPM. You could put the planetarium on top and it would spin slowly.

Thank you so much for the idea! I was trying to figure out a way to make a portable planetarium for my astronomy class and found your instructions. The kids have had a blast designing and building the parts. We are using a steel mixing bowl and house current for power. We have also mounted the bowl and base on an old telescope tripod. The theater is a black tarp in the shape of a dome that we inflate with a large fan. We are still working on all the parts and will post pictures of the end results as we get them done. The comments from others have been very helpful too. Science never sucks!

Hey Matt, awsome project, congratz. I did my own based on your design, only a few changes, power source from the wall socket, small things like that. I used a 3w Blue Led, it gives u more of a star effect i think, it's less "light" but more defined dots. Also, adding a LM317T is great to get constant controlled current is a good idea. Also, instead od rivets, just bolts and nuts, so you can open it an fix it just in case. My little niece loved it, i really appreciate your idea Matt.. keep'em coming.

Glad you liked it and that it went well for you. Mine does open of course, it eats batteries pretty quickly. There are a few screws around the rim of the dome that allow it to open up. This was a really early project of mine, before I knew much about metalwork or electronics, but it still turned out really well. I built a 2nd one a year later using a power inverter to let me wall power it, but it didn't turn out nearly as nice as this one, unfortunately. The higher power LED I used had a square emitting surface inside it so all the stars turned out square as well! And the switch mode supply I put inside it makes whiny noises when its running.

Matt! That's an extremely great idea! I've already done one of those with a shoe box, and a flashlight (as the paper doesn't reflect light). It worked out of the box! Then, I bought one of those http://www.prlog.org/11168760-star-sky-projector-lamp.jpg Anyway, it was worse then I expected. I like the way you did yours, and I'll do one this weekend. I'll buy the LED's tomorrow. Great Instructable! I'm planning to include a blue light inside the box also, so that if I want a "calming" and "relaxing" light, I could use it! :D

if you added a Fresnel lens then the possibility of adding more light sources and maintaining ledgeble constellations easy, there relatively cheat usually made of plastic so you could cut it to fit nicely inside